So we are using the past tense stems, but we don’t need to add the extra vowel to the beginning anymore, is that right? And so we just make the first syllable the stressed syllable (for these short verbs)?
I was also expecting the γάμμα from the past tense of τρώω as part of the stem for this one...is this verb just irregular, or is there some pattern here that would also apply to other verbs?
Τρώω is an irregular verb indeed. Not all verbs form past tenses with an added vowel in the beginning. Also, the form φάει is called the infinitive form (works differently from the one in English, but, like the one in English, it does not change) and is used for the simple perfect and the past perfect tenses, so it's another story altogether.
The best thing to do is probably find the conjugation tables for the verbs you'll see in this course and study them; then you'll see the patterns emerge. e.g.
(present - imperfect - simple past - simple perfect)
θέλω - ήθελα - θέλησα - έχω θελήσει
πίνω - έπινα - ήπια - έχω πιει
πάω/πηγαίνω - πήγαινα - πήγα - έχω πάει
δίνω - έδινα - έδωσα - έχω δώσει
βλέπω - έβλεπα - είδα - έχω δει
τρώω - έτρωγα - έφαγα - έχω φάει
κάνω - έκανα - έκανα - έχω κάνει
Please note that the above are examples of active voice verbs only. There are some patterns but you can't just guess their conjugation/tenses, you'll have to start by studying them individually and as you become familiar with more and more of them you'll be able to start guessing. :)
Thanks so much for this post!
Incidentally, I just ordered 201 Greek Verbs on Amazon. I also wish to express my deepest gratitude to all contributors for continuing to encourage us on our Greek learning adventure. Greek is quite a challenge for me but so very enjoyable! Next, complete the current tree, get a Greek reader for beginners, and see if I can test out of the next tree in 2020. Duolingo rocks!